The present disclosure generally relates to systems and methods for preparing cement or gypsum products, and more particularly relates to improved systems and methods for controlling a line speed of a conveyor system during product changeovers in a wallboard production line.
Conventionally, gypsum products, such as calcium sulfate dihydrate, are prepared with typical basic ingredients, including calcined gypsum, such as calcium sulfate hemihydrate or anhydrite, and water. A slurry mixer is typically used for supplying agitated gypsum slurry to the wallboard production line. Several types of gypsum wallboard manufacture are described in co-assigned U.S. Pat. Nos. 6,494,609 and 6,986,812; both of which are incorporated by reference.
As is well known in the art, a mixer is provided for uniformly dispersing calcined gypsum into water to form a slurry, and then the slurry is cast into a desired shaped mold or onto a surface to allow the slurry to set and form hardened gypsum by chemical reaction of the calcined gypsum with water. A lightweight gypsum product is provided by uniformly mixing aqueous foam into the slurry to produce air bubbles. This results in a uniform distribution of voids in the set gypsum product when the bubbles are confined in the slurry before the gypsum hardens.
As the slurry travels downstream toward a forming plate on a conveyor system, a thickness of the slurry is determined by a predetermined location of the forming plate above a conveyor belt. Depending on a mass rate of the slurry traveling on the conveyor belt relative to a line speed of the conveyor system, maintaining a generally laminar flow of the slurry before the forming plate is not readily achievable. An optimal line speed generally refers to a maximum possible speed that the conveyor system can support without forming a disruptive slurry head immediately before the forming plate.
When the line speed is too fast relative to the mass rate of the slurry traveling on the conveyor belt, excessive slurry that cannot pass through the forming plate creates the slurry head in front of the forming plate, causing uneven accumulation and frequent clogging of the forming plate in the production line. Specifically, when the product changeover is initiated, a composition or density rate of the gypsum product changes and also alters the mass rate of the slurry based on the product changeover requirements.
Therefore, there is a need for controlling the line speed of the conveyor system during the product changeovers such that the optimal line speed is maintained for the laminar flow of the slurry.
As the slurry advances on the conveyor belt, and is deposited between two paper liners below the forming plate, a thickness of the wallboard being formed is equalized. After passing through the forming plate, the formed wallboard continues to travel on the conveyor belt for a predetermined period to allow the gypsum in the wallboard to set. Next, the set continuous strip of wallboard is cut into predetermined lengths, forming panels or boards, and each cut board then passes through a hydration section and subsequently a drying section having an oven or kiln on single or multiple decked roller conveyors, such that heated air is blown across an upper and lower faces of the board for drying.
However, when gaps between adjacent boards are too wide, exposed edges of the board become parched or toasted by the heated air, and the toasted edges tend to warp, buckle, pop, crumble or otherwise distort the board due to uneven drying. As a result, the boards are sent through the drying kiln side-by-side or end-to-end to reduce the exposed edges and any associated distortions of the boards. While the hydration section and the drying section are part of the conveyor system as a whole, each section has its own line speed for the corresponding conveyor belt.
Therefore, there is a need for controlling the line speed of the conveyor system for the cut wallboard panels going into the kiln such that the adjacent boards are touching each other in an end-to-end relationship to prevent toasting the edges during heat treatment.